Example: Configuring BGP to Advertise Inactive Routes

Step-by-Step Procedure

The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.

To configure Device R2:

1. Configure the device interfaces.

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   [edit interfaces]
   user@R2# set fe-1/2/0 unit 0 family inet address 10.0.0.2/30
   user@R2# set fe-1/2/1 unit 0 family inet address 10.0.0.5/30
   user@R2# set lo0 unit 0 family inet address 192.168.0.2/32
   

2. Configure the EBGP connection to Device R1.

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   [edit protocols bgp group to_R1]
   user@R2# set type external
   user@R2# set neighbor 10.0.0.1 peer-as 100
   

3. Configure the EBGP connection to Device R3.

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   [edit protocols bgp group to_R3]
   user@R2# set type external
   user@R2# set neighbor 10.0.0.6 peer-as 300
   

4. Add the advertise-inactive statement to the EBGP group peering session with Device R3.

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   [edit protocols bgp group to_R3]
   user@R2# set advertise-inactive
   

5. Configure the static route to the 172.16.5.0/24 network.

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   [edit routing-options static]
   user@R2# set route 172.16.5.0/24 discard
   user@R2# set route 172.16.5.0/24 install
   

6. Configure the autonomous system (AS) number.

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   [edit routing-options]
   user@R2# set autonomous-system 200
   

Results

From configuration mode, confirm your configuration by entering the show interfaces, show protocols, show policy-options, and show routing-options commands. If the output does not display the intended configuration, repeat the instructions in this example to correct the configuration.

user@R2# show interfaces
fe-1/2/0 {
    unit 0 {
        family inet {
            address 10.0.0.2/30;
        }
    }
}
fe-1/2/1 {
    unit 0 {
        family inet {
            address 10.0.0.5/30;
        }
    }
}
lo0 {
    unit 0 {
        family inet {
            address 192.168.0.2/32;
        }
    }
}

user@R2# show protocols
bgp {
    group to_R1 {
        type external;
        neighbor 10.0.0.1 {
            peer-as 100;
        }
    }
    group to_R3 {
        type external;
        advertise-inactive;
        neighbor 10.0.0.6 {
            peer-as 300;
        }
    }
}

user@R2# show routing-options
static {
    route 172.16.5.0/24 {
        discard;
        install;
    }
}
autonomous-system 200;

If you are done configuring the device, enter commit from configuration mode.

Purpose

On Device R2, make sure that the 172.16.5.0/24 prefix is in the routing table and has the expected active path.

Action

user@R2> show route 172.16.5

inet.0: 7 destinations, 8 routes (7 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

172.16.5.0/24      *[Static/5] 21:24:38
                      Discard
                    [BGP/170] 21:21:41, localpref 100
                      AS path: 100 I, validation-state: unverified
                    > to 10.0.0.1 via fe-1/2/0.0

Meaning

Device R2 receives the 172.16.5.0/24 route from both Device R1 and from its own statically configured route. The static route is the active path, as designated by the asterisk (*). The static route path has the lowest route preference (5) as compared to the BGP preference (170). Therefore, the static route becomes active.

Purpose

On Device R2, make sure that the 172.16.5.0/24 route is advertised toward Device R3.

Action

user@R2> show route advertising-protocol bgp 10.0.0.6


inet.0: 6 destinations, 7 routes (6 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
  172.16.5.0/24           Self                                    100 I

Meaning

Device R2 is advertising the 172.16.5.0/24 route toward Device R3

Purpose

Make sure that the 172.16.6.0/24 prefix is in Device R3’s routing table.

Action

user@R3> show route 172.16.5.0/24

inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

172.16.5.0/24      *[BGP/170] 00:01:19, localpref 100
                      AS path: 200 100 I, validation-state: unverified
                    > to 10.0.0.5 via fe-1/2/1.0

Meaning

Device R3 has the BGP-learned route for 172.16.5.0/24.

Purpose

See what happens when the advertise-inactive statement is removed from the BGP configuration on Device R2.

Action

1. On Device R2, deactivate the advertise-inactive statement.

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   [edit  protocols bgp group to_R3]
   user@R2# deactivate advertise-inactive 
   user@R2# commit
   

2. On Device R2, check to see if the 172.16.5.0/24 route is advertised toward Device R3.

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   user@R2> show route advertising-protocol bgp 10.0.0.6
   
   

   As expected, the route is no longer advertised.

3. On Device R3, ensure that the 172.16.5/24 route is absent from the routing table.

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   user@R3> show route 172.16.5/24
   
   

Meaning

Device R1 advertises route 172.16.5/24 to Device R2, but Device R2 has a manually configured static route for this prefix. Static routes are preferred over BGP routes, so Device R2 installs the BGP route as an inactive route. Because the BGP route is not active, Device R2 does not readvertise the BGP route to Device R3. This is the default behavior in Junos OS. If you add the advertise-inactive statement to the BGP configuration on Device R2, Device R2 readvertises nonactive routes.